Terry Fields, who has died of lung cancer aged 71, was a rebel Labour MP from the Militant Tendency and a thorn in the side of the then Labour leader Neil Kinnock; for the last months of his nine years in the House of Commons, he sat as an independent. He was also a firefighter, and a respected activist in the Fire Brigades Union (FBU).

During the 1970s he was prominent in Liverpool Labour politics, which became bitterly divided during the decade, with the rise of the Militant Tendency. Militant represented a new and alarming threat to the Labour party leadership, because, while other Trotskyist-inspired groups rejected involvement with Labour, Militant embraced "entryism", a policy of joining the party and bringing it round to its point of view.

Militant advocated uncompromising socialist policies and excoriated Labour leaders who thought that adopting them was either wrong or simply electoral suicide. The nature of the debate was illustrated by Labour's 1980 special conference at which Fields said: "We need coordinated action by the whole of our class to get the Tories out, and the democracy that is being pumped out in the capitalist press is their democracy, not ours. We will found a new democracy when we have created a socialist state in this country... To the weak-hearted, the traitors and cowards I say: 'Get out of our movement. There is no place for you. Cross the House of Commons ...' "

The next speaker, former chancellor Denis Healey, to shouts of "out, out", replied: "We certainly will not win the next election if ... instead of meeting the real needs of people, we go on ideological ego trips or accept the clapped-out dogmas which are now being trailed by the toytown Trotskyists of the Militant group ..."

The new intake of Labour MPs in June 1983 included two from the Militant Tendency - Fields, representing Liverpool Broadgreen, and Dave Nellist, for Coventry South East. From then on, Fields' weatherbeaten face, topped by trademark dark glasses, was seldom out of the newspapers. He and Nellist shared a small office, after Nellist had managed to extract himself from the one he was uncomfortably sharing with a fellow newcomer to the Labour benches called Tony Blair.

Later that year, Labour's conference elected a new leader, Kinnock, who was determined that Labour should expel Militant from its ranks, and for years his leadership was dominated by the long, angry, litigious debate this entailed.

Fields was at the centre of it, and remained a key figure in Liverpool politics as the Militant Tendency took over the city council, which led to the famous 1986 Labour conference confrontation between Kinnock and the council's deputy (but de facto) leader, Derek Hatton.

One of the councillors, Tony Mulhearn, president of Liverpool City Labour party at the time, remembers Fields as "an outstanding MP who took advice from his constituency and lived the same life as the people who elected him". He kept his election promise to take only the equivalent of his fire-fighter's wage, not his whole MP's salary, giving the balance to community causes and trade unions.

Nellist recalls that he "never asked anyone to do anything he would not do himself," citing as an example Fields' imprisonment in 1991 for refusing to pay his poll tax. "He was effectively saying to the government: take me first." Kinnock's comment at the time was: "Lawmakers must not be lawbreakers." Fields went to prison for 60 days.

Kinnock finally succeeded in having Fields and Nellist expelled at the end of the year - the first to be thrown out of the parliamentary party since 1949. They continued as independents, and at the 1992 election, both faced official Labour opponents and lost their seats.

Born in Bootle, Fields joined the Merseyside fire service when he was 20, and was still working there when elected an MP 26 years later. By then he had become a fire safety officer and Merseyside's representative on the executive of the union. He is remembered with admiration in FBU circles, general secretary Matt Wrack recalling his "honour, honesty and humour".

His insistence on taking only his firefighter's wage while in the Commons was a principled stand which left him poorer than most former MPs. "His main activity then was to survive," says Mulhearn. He managed a Liverpool pub, the Mayflower, until he retired.

He did not return to frontline politics, and never joined the party which replaced Militant, the Socialist party. He felt, says Mulhearn, that it was time for younger people to take over. He did, however, do advice work for the Citizens Advice Bureau and, from working on his allotment, he became a spokesman for fellow allotment holders. In 2002 he was briefly in the public eye again, when - once a firefighter, always a firefighter - he ran into a burning house in order to drag a woman to safety.

Friends describe a kind and essentially humble man who enjoyed singing country music and was in a skiffle group in the 1960s.

He is survived by his wife Maureen; his children, Michael, Paula and Stephan; 10 grandchildren; and one great-grandchild.

· Terence Fields, trade unionist and political activist, born March 8 1937; died June 28 2008